diff options
| author | Matthew Ahrens <[email protected]> | 2019-06-12 13:13:09 -0700 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2019-06-12 13:13:09 -0700 |
| commit | d9b4bf0665a0b1a7af2bbb34c60bca612956022d (patch) | |
| tree | c90c5694edb1dd655ecbe46caac64c2be50229d7 /module/zfs/dmu.c | |
| parent | d9cd66e45f285356624d26eb92e10e2baf2738ee (diff) | |
fat zap should prefetch when iterating
When iterating over a ZAP object, we're almost always certain to iterate
over the entire object. If there are multiple leaf blocks, we can
realize a performance win by issuing reads for all the leaf blocks in
parallel when the iteration begins.
For example, if we have 10,000 snapshots, "zfs destroy -nv
pool/fs@1%9999" can take 30 minutes when the cache is cold. This change
provides a >3x performance improvement, by issuing the reads for all ~64
blocks of each ZAP object in parallel.
Reviewed-by: Andreas Dilger <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Matthew Ahrens <[email protected]>
External-issue: DLPX-58347
Closes #8862
Diffstat (limited to 'module/zfs/dmu.c')
| -rw-r--r-- | module/zfs/dmu.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/module/zfs/dmu.c b/module/zfs/dmu.c index 2d6740576..b4131d917 100644 --- a/module/zfs/dmu.c +++ b/module/zfs/dmu.c @@ -81,6 +81,13 @@ int zfs_dmu_offset_next_sync = 0; */ int zfs_object_remap_one_indirect_delay_ms = 0; +/* + * Limit the amount we can prefetch with one call to this amount. This + * helps to limit the amount of memory that can be used by prefetching. + * Larger objects should be prefetched a bit at a time. + */ +int dmu_prefetch_max = 8 * SPA_MAXBLOCKSIZE; + const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES] = { {DMU_BSWAP_UINT8, TRUE, FALSE, FALSE, "unallocated" }, {DMU_BSWAP_ZAP, TRUE, TRUE, FALSE, "object directory" }, @@ -668,6 +675,11 @@ dmu_prefetch(objset_t *os, uint64_t object, int64_t level, uint64_t offset, } /* + * See comment before the definition of dmu_prefetch_max. + */ + len = MIN(len, dmu_prefetch_max); + + /* * XXX - Note, if the dnode for the requested object is not * already cached, we will do a *synchronous* read in the * dnode_hold() call. The same is true for any indirects. @@ -2629,6 +2641,10 @@ module_param(zfs_dmu_offset_next_sync, int, 0644); MODULE_PARM_DESC(zfs_dmu_offset_next_sync, "Enable forcing txg sync to find holes"); +module_param(dmu_prefetch_max, int, 0644); +MODULE_PARM_DESC(dmu_prefetch_max, + "Limit one prefetch call to this size"); + /* END CSTYLED */ #endif |